Literature Review 1 of 2
Loss of Recent Memory After Bilateral Hippocampal Lesions
Despite being fundamental to human cognition, memory remained one of the least understood brain functions in the mid-20th century, an era without MRI or other advanced technologies. The paper "Loss of Recent Memory after Bilateral Hippocampal Lesions," written in 1957 by William Scoville and Brenda Milner, is a landmark study that revealed key insights about the neurological basis of memory and is one of the most important studies in the field of neuroscience. In their experiment, the authors investigated why patients like Henry Molaison (Patient H.M.) were experiencing seizures, psychotic symptoms and other brain-related illnesses, through a surgical approach involving the removal of his hippocampus. This groundbreaking operation led to discoveries that revolutionized our understanding of memory, and the discoveries yielded from it changed the field of neuroscience forever.
To understand this study, it is helpful to consider some background information. At the time, there was not much known about mental illnesses or the different roles of parts of the brain. This led doctors to perform invasive procedures such as lobotomies, or removing parts of the brain, to try to cure disorders like epilepsy or bipolar disorder. However, the hippocampus actually plays a crucial role in memory, which is much more significant than previously thought. Additionally, there are many distinct types of memory within the more general short and long-term branches, such as working memory, which is used when one does mental math; semantic memory, the long-term memory of facts, concepts, and language; and episodic memory, which is memory used to recall significant events or moments (going to a place for the first time) that you experienced. Some key terminology in this paper is anterograde amnesia, a condition in which a person can't form new memories but remembers previous memories before surgery; medial temporal lobe (MTL), a brain lobe which includes the hippocampus; and bilateral, which means on both sides of something.
In their experiment, scientists lesioned the patients' MTL and hippocampus, then observed their behaviors and conducted psychiatric assessments of their personalities, intelligence, memory. In the surgery, they removed the hippocampus and amygdala. Patient H.M.'s seizures stopped, but he unexpectedly developed anterograde amnesia, meaning he could no longer form new memories. He retained long-term semantic and episodic memories, but only had an effective working (short-term) memory after his surgery, suggesting that damage to the hippocampus impairs memory. The most important patient in this study is H.M., but others were also included in the paper who had varying levels of neurological problems, who had no changes in personality or IQ, but were similarly unable to form any new memories due to anterograde amnesia after the surgery.
There are a few notable takeaways from this paper. First, the hippocampus plays a significant role in memory by sending new short-term memories for permanent long-term storage. Furthermore, the more of the MTL that is destroyed, the more severe the amnesia is. The operation raised a substantial ethical concern about brain surgeries, particularly those that are as invasive as removing an entire part of the brain. This case highlighted the importance of informed consent and the risks of radical brain surgeries as well as that mental illnesses should not be treated with invasive brain surgeries like lobotomies.
This paper marked a turning point in neuroscience and neuroanatomy. However, it faces some limitations. Some shortcomings are that the procedures and content described in the paper are slightly outdated, as it was published in 1957. Further, since it is largely centered around a case study, not all the results can be generalized. While some conclusions may be limited by the technology and understanding of the time, this study is still very useful because without it, we wouldn't know the crucial role that the hippocampus plays in making and consolidating new memories. Despite its age, the paper is relatively accessible and provides foundational knowledge about the hippocampus and memory, illustrating that every part of the brain is important, and defining the basics of today's modern neuroscience.
Literature Review 2 of 2
Creating a False Memory in the Hippocampus
False memories can form when the brain fills in gaps in memory, often due to sleep deprivation, hallucinations, or the brain's innate tendency to construct coherent narratives. However, the deliberate creation of artificial false memories remained largely unexplored until the 2013 study "Creating a False Memory in the Hippocampus" by Steve Ramirez et al. In this experiment, the scientists investigated whether they could find a memory in the brain and manipulate it, and whether it was possible to alter memories using light. The scientists employed optogenetics, a specialized technique in which brain cells are activated and deactivated with light, enabling them to "turn on" a memory and investigate whether a false fear memory could be created. They identified specific memory engrams, which are neurons that control a specific memory. To activate the memories using light, they used a light-sensitive protein called channel rhodopsin, which acted like an "on-off" switch for the engram. Through its findings, this study paved the way for a modern understanding of the constructive and vulnerable nature of memory.
The researchers conducted this study by using mice as model organisms. By inserting a light-sensitive protein called channel rhodopsin-2 into the dentate gyrus of a mouse using a virus, they were able to create a light switch to control the brain. Using this switch, they could activate specific memories. To test this, scientists placed mice into two distinct environments, labeled Context A and Context B. Context A was a safe environment with no stressors. However, in Context B, the mice were given a foot shock when exploring the box while the memory from Context A was activated. They were then placed into box A, where they displayed freezing behavior, indicating that they felt fear despite never being shocked in Context A. This demonstrates that the mice had formed a false memory based on the optogenetic reactivation of Context A while in Context B.
The study effectively conveyed how memories are encoded and retrieved in the brain, providing novel insight on how it can be manipulated. It had a strong experimental design, with each part of the experiment serving a clear purpose, helping to demonstrate the results accurately. On the other hand, the experiment was not as effective in defining more complicated concepts. Although the diagrams appear modern, they can still be somewhat difficult to understand, especially for those unfamiliar with optogenetics and how the brain works.
This experiment is important to the field of neuroscience as it shows that memories can be altered and changed. It also opens up more exploration into optogenetics, a field usually dismissed in the past, and shines a spotlight on memory creation and the ethical risks behind it if it is used in human minds. The experiment also rewrote what memory was, and it helped neuroscientists discover more about the brain, explaining in detail how memories can be edited and how fake memories are formed. This provides more information on memory for neurologists and can be useful in the future, opening up new possibilities.